A third vaccine against Covid-19 has been approved for use in the UK.

The vaccine, made by US firm Moderna, was given the green light by the Medicines and Healthcare products Regulatory Agency (MHRA). Trials of the jab show it is 94 per cent effective in preventing infection from the virus.

However, the doses ordered by the UK are not expected to be available until the spring after the pharmaceutical firm expands its production capability.

Health Secretary Matt Hancock said: “This is further great news and another weapon in our arsenal to tame this awful disease.

“We have already vaccinated nearly 1.5 million people across the UK and Moderna’s vaccine will allow us to accelerate our vaccination programme even further once doses become available from the spring.

“While we immunise those most at risk from Covid, I urge everyone to continue following the rules to keep cases low to protect our loved ones.”

The Moderna vaccine functions in a similar way to the Pfizer vaccine, with both using a molecule known as mRNA, which the body uses as instructions to build proteins in cells. In this case, the mRNA contains the genetic sequence for the cells to build the virus’ unique markers, or antigens.

This causes an immune response which allows the body to develop immunity against infection by the actual virus. It is 94 per cent effective at preventing the disease, including in the elderly.

Following months of clinical trials, the MHRA has now approved the vaccine for use in humans after accepting the recommendation of the Commission on Human Medicines.

The government had previously agreed to purchase seven million doses of the vaccine, which will now be increased to 17 million.

These will be delivered later this year, in line with an agreement struck with the firm in 2020.

For now, the Pfizer and AstraZeneca vaccines will continue to be rolled out across the UK, with Boris Johnson announcing an intention for two million people a week to be vaccinated against Covid. This is more than all the people in the country who have currently been vaccinated – 1.5 million.